Advanced design of 3D knitted padding for wearable cushioning in knee protector | Scientific Reports

Scientific Reports volume 15, Article number: 11091 (2025) Cite this article

Metrics details

Wearable cushioned products protect the body during sporting activities or work-related activities. Cushioning paddings made of elastomeric materials are used to absorb impact forces. The paddings are usually inelastic, which could be challenging to accommodate the movement of knee joints and lead to displacement. In this study, a new knitted composite which consists of soft surface layers, a shock absorption middle layer made of monofilament and silicone inlays and additional elastic inlays in the surface layer to accommodate the body contours is developed. The three-layer structure is knitted as 3D knee paddings in a single process. The air permeability, mechanical properties, and subjective wear comfort of the knitted paddings and their impact on muscle activity are evaluated and compared with those of commercially available elastomeric knee paddings. The results show that the knitted padding with a silicone inlay can better absorb impact forces than that without the inlay showing a 14% increment. The 3D knitted padding is perceived to be more soft, elastic and bendable, with a better fit and wear comfort, with more slip resistance than the elastomeric padding with a similar thickness. The outcomes can act as a good reference for the development of textile cushioning materials.

Cushioning materials are integral to personal protective devices (PPDs) such as helmets, motorcycle jackets, boxing gloves, shin guards, and knee and elbow pads. These materials safeguard the body against the forces from potential impact during physical activities. Elastomeric materials such as foam rubber (latex, neoprene) and cellular polymer [polypropylene (PP), polyethene (PE), ethylene–vinyl acetate (EVA), and polyurethane (PU)] are commonly used in PPDs for cushioning purposes1,2,3. The advantage of using elastomeric materials is that they are light in weight and can be customised with different densities and stiffness levels to suit different end-uses4. The paddings are laminated with fabrics or embedded in the products to give a better hand feel. Recently, 3D printed structures have been adopted to enhance the energy absorption efficiency5. However, these materials tend to be rigid and thick, which can limit the range of motion, particularly around the joint areas, thereby inhibiting body movement. Besides, the low air permeability and poor moisture transfer and heat dispersion of the elastomeric materials trap sweat and heat and thus result in low wear comfort. Therefore, it is crucial to enhance the quality of PPDs, starting by examining the cushioning materials used.

The knees have a complex structure and carry a significant load during movement6. A good knee brace or knee sleeve is essential to absorb and distribute the impact force over a larger area to reduce direct stress on the knee joint7. A knee brace or knee sleeve can prevent injuries or protect the injured area from further damage, thus enabling wearers to move during athletic activities or participate in sports with greater confidence and wear comfort8. Apart from absorbing impact, the cushioning padding has to be flexible to avoid restricting knee movement9. The knee padding should conform to the shape of the knees to prevent displacement during activities10. In order to accommodate the knee contours, conventional cushioning materials are trimmed, moulded, sewn or laminated to the desired shape. In the production process, a large amount of resources are consumed and an immense volume of waste is created. Moreover, the thick inelastic padding cannot cater to the variations in skin strain during knee movement, thus leading to slippage, displacement and discomfort. Although there are many different types of knee braces or knee sleeves in the market, there is no device that considers sustainability during production with good wear comfort.

Spacer fabrics have been introduced to the market as a cushioning material for more than 10 years11,12. These fabrics have a 3D structure with filaments in the middle connective layer that holds the two outer layers together. The 3D structure allows good energy absorption whereas the knitted structure formed by the interloping of yarns provides spacer fabrics with good air-permeability, heat dispersion and moisture transfer properties13,14. Spacer fabrics have been used for bra-cups, car seats, bedding, shoe uppers, medical garments, etc. to enhance ventilation and wear comfort15,16,17,18. However, compared to foams or cellular polymers, it is more difficult to control the thickness and mechanical properties of spacer fabrics. A thin spacer can be too weak to withstand high stress and collapses easily. Therefore, the use of spacer fabrics as knee padding is not ideal. On the other hand, a tight fabric structure with thick and stiff yarns leads to a rigid and stiff fabric and sacrifices flexibility, cushioning properties and wear comfort. Therefore, even though spacer fabrics are more breathable, they cannot be used in lieu of conventional types of cushioning materials.

Several research studies have been conducted to investigate the properties and improve the performance of spacer fabrics. Liu et al.19,20 investigated the compression behaviour of both warp and weft knitted spacer fabrics. They confirmed that the fabric thickness and spacer structure affect the compression properties of spacer fabrics. Asayesh and Amini21 found that spacer fabrics with a surface layer that consists of all knit stitches can absorb more energy and demonstrate better resiliency than those that consist of knit and miss stitches. Apart from changing the structure of the spacer fabric surface, spacer fabric can be integrated with other materials to enhance their cushioning performance. Hamedi et al.22 incorporated a shape memory alloy into the spacer layer to increase energy absorption capacity. Jiang et al.23 filled spacer fabric with silicone rubber to improve the load capacity and impact resistance. Xu et al.24 impregnated warp knitted spacer fabric with a shear thickening fluid to increase energy absorption. Yu et al.25 used elastic yarn as the inlay in the surface layers to increase the thickness and compression energy absorption of spacer fabrics and inserted silicone tubes in the middle layer as the inlay to enhance the impact force absorption properties26,27. The additional materials inserted into the structure of the spacer fabric have a positive impact and these studies provide direction for the further development of textile cushioning.

This study aims to develop a novel 3D knitted structure with curvature and shape of a knee padding formed in the knitting process so as to increase the wearing comfort, facilitate physical body motions and provide a more environmentally friendly solution for padding production. The study approach is shown in Fig. 1. The novel design of the padding is based on the outcomes of previous studies on the curvature control of spacer fabric and silicone inlay reinforcement27,28. The padding is made by using yarns with the desired oval shape and curvature in a single process to minimise waste and shorten the production process. As the knitted padding is 3D in shape, the inner and outer faces of the padding are not balanced. The physical and mechanical properties of the 3D knitted padding are measured to investigate this novel three-layer structure. The feasibility of improving knee protection by using the proposed 3D knitted structure will then be evaluated.

The idea of the 3D knitted padding development.

A novel padding with high cushioning ability and curvatures that accommodated the body contours was directly fabricated with yarn in a single process. SDS-ONE APEX3 (Shima Seiki, Japan) software was used to design the knitting pattern and a computerised flat knitting machine (SWG091N210G, Shima Seiki, Japan) was used to knit the padding.

The padding has a three-layer structure (Fig. 2). The two outer layers form a jersey structure which provides good air permeability. Adopting the same approach as Yu et al.16, the oval shape of the padding was formed by adjusting the number of wales in each course. In order to form a curvature on the padding to accommodate the shape of the knee, an irregular structure is needed. The inner face that is in contact with the skin was inlaid with elastic yarn for contraction in the course-wise direction. The ratio of the number of courses of the inner layer to the outer layer was 2:3 to provide curvature in the wale-wise direction. The curvature allows the padding to accommodate the shape of the knee when standing up straight. The knitted structure provides the padding with good elasticity. When the knees bend, the knee padding can extend and accommodate the changes in the knee contours.

Knitted padding design.

Similar to conventional spacer fabric, the middle layer consists of monofilament yarns formed with tuck and miss stitches to support the structure and provide cushioning. In order to enhance impact force absorption, silicone hollow tubes were inserted into the middle layer by using front and back tuck stitches to provide extra reinforcement to the 3D structure. The silicone hollow tubes were inlaid in every four courses of the inner face. Figure 3 shows yarn path diagrams for knitting the paddings and the views of the inner and outer faces and the cross-section of the knitted paddings with and without the silicone inlaid. Although the silicone tube is inlaid in the middle layer, the surface structure and appearance are also affected. The use of a silicone tube inlay in a curved spacer fabric structure is innovative for achieving cushioning performance. This study further investigates the effects through the mechanical properties of the silicone tube inlay.

(a) Yarn path diagram for knitting of the 3D shaped paddings and the views the paddings (b) without silicone inlaid and (c) with silicone inlaid.

A total of six 3D knitted padding samples were fabricated. The sample details are presented in Table 1. All of the samples are made with the same type of yarn for the surface layer and the same elastic inlay yarn. The stitch tension and spacer layer fabrication pattern are the same. The samples also have the same oval shape and a similar curvature to accommodate the contours of the knees. The samples are designed to evaluate two effects from: (1) the type of monofilament spacer yarn and (2) silicone tube reinforcement. Four samples, PA1, PA2, PET1 and PET2, were constructed by using polyamide and polyester monofilament spacer yarn with two different thicknesses without the silicone tube inlay, and two samples, SPA and SPET, were made with silicone tubes inserted in the middle connective layer. Silicone hollow tubes which have 1 mm in diameter and 0.5 mm in diameter of the hollow were used. A silicone tube was carried by a yarn carrier with a wider opening and inlaid to the knitted structure during the knitting process. All of the samples were allowed to relax for 1 week after they were taken out from the knitting machine and stored in a standard environmental condition (20 ± 2 °C, 65 ± 2% relative humidity) for at least 24 h before testing.

Three padding samples, F1, F2 and F3, of commercially available knee sleeves were also used for comparison purposes (Fig. 4). The commercial samples have different thicknesses and compositions. F1 is made of neoprene punched with many small holes and laminated with a thin single jersey knitted fabric on one side and a felted knitted fabric on the other side. F2 is a thick multi-layer structure with a thick layer of ethylene vinyl acetate (EVA) foam embedded between two thin neoprene layers laminated with a single jersey and a felted knitted fabric, respectively. F3 is made of EVA foam laminated with a single jersey knitted fabric on the outer surface.

Images of commercial knee padding (a) Sample F1, (b) Sample F2 and (c) Sample F3.

The air resistance, compression and impact force absorption of the samples were evaluated. Three specimens were prepared for each evaluation. The air resistance was tested by using an air permeability tester (KES-F8, Kato Tech Co., Ltd, Japan) with an air vent area of 6.281 cm2 and an air volume of 2 cm/s. Five points on both sides of each specimen were measured. The compression was measured by using a compression tester (KES-G5, Kato Tech Co., Ltd., Japan) with a circular testing area of 2 cm2 at a compression rate of 0.2 mm/s and maximum stress of 49 kPa. The centre of the inner side of each specimen was tested for compression. The impact force absorption of the samples was evaluated by using a set-up with a dynamic load cell mounted at the bottom and placed underneath the tested samples, which follows the standard testing method in ASTM D2632 to measure the resilience properties of rubber through vertical rebound. Two plies of each sample were used to reach the standard testing thickness of 15 mm. During the testing, a ball bearing was dropped from a tube inside the instrument at a height of 400 mm onto the samples that were placed on top of the load cell. Ten random locations on the outer side of the specimens were tested. The maximum impact force and reaction time on the materials can be accurately measured and recorded by using the load cell (Dytran series 1051, Dytran Instruments, Inc.) and its data acquisition system (Dewesoft X). The force reduction percentage (FR) was calculated by using:

where Fx is the peak force (N) of the tested samples and Fo is the peak force of the ground surface (N).

A wear-trial experiment with 10 participants—5 males and 5 females, was conducted to investigate the effect on muscle activity and subjective sensation caused by the different knee paddings. The information of the participants is shown in Table 2. A knee sleeve with a pocket for the insertion of the padding was designed, as shown in Fig. 5a. The three commercial paddings, F1, F2 and F3 and two plies of knitted padding with a silicone tube inlay, SPET, were inserted into the knee sleeve for evaluation (Fig. 5b). Velcro was used as the fastening to allow adjustment of the fit of the knee sleeve based on the lower limb dimensions of the subjects (Fig. 5c).

(a) Dimensions of knee sleeve for wear trial experiment, (b) knee sleeve with pocket for inserting padding, (c) participant wearing pair of knee sleeves, (d) sEMG sensors and electrodes on the leg of a participant, (e) three muscles for sEMG measurements, (f) rating scales for subjective assessment of knee paddings, and (g) protocol of wear-trial experiment.

In the beginning, the participants had to complete a 3-min warm-up exercise and practice the wear trial exercises before the experiment to avoid injury and become accustomed to the task. A wireless myoelectric signal measurement system (Ultium EMG, Noraxon, USA) was used to record and process the surface electromyography (sEMG) signals. The sEMG signals were collected at a sampling rate of 2000 Hz and band-pass filtered between 10 and 500 Hz. The skin of the dominant leg was prepared, and disposable silver/silver chloride (Ag/AgCL) surface electrodes (Hex Dual Electrodes, Noraxon, USA) were placed on the belly of the tested muscles (Fig. 5d). Knee movement is mainly associated with the quadriceps, hamstrings, and gastrocnemius muscles29,30. Therefore, the sEMG signals on the (1) vastus lateralis (VL), (2) biceps femoris (BF) and (3) gastrocnemius lateralis (GL) muscles of the dominant leg of the participant were measured (Fig. 5e). Several maximum voluntary contractions (MVCs) of the leg muscles were measured for normalisation purposes31. The maximum 1000 ms root mean square (RMS) value across the MVC trials for each muscle was regarded as the maximum voluntary electrical activation (MVE). The amplitude of the sEMG signals was normalised with MVE and expressed as %MVE.

The experiment involved three exercises: (1) walking and running on a treadmill, (2) vertical jumping and (3) squatting, which correspond to the training movements of volleyball and basketball players32. In the first exercise, the participants had to walk for 1 min at the speed of 3 km/h, run for 3 min at a rate of 6 km/h and walk for another minute on the treadmill (Horizon TR5.0, Johnson Fitness, Japan). The second exercise was to perform 5 vertical jumps in which the participants could squat down a bit and jump up vertically with the fingertips reaching at least 30 cm from the standing reach height. The last exercise was squatting five times. The participant kept his/her feet apart at shoulder-width distance and arms straight, squatting down completely and holding the position for 3 s. The participants were asked to subjectively rate from 0 to 10 on the softness, elasticity, flexibility, fit, slippage, and wear comfort of the knee paddings before and after the exercises as shown in Fig. 5f. The experiment protocol is summarised and presented in Fig. 5g. Each participant underwent the four conditions with the different paddings as well as a control condition or without padding. The order of the experiment with the five different conditions was randomised to minimise any potential order effect. The overview and procedures of the experiment were explained to each participant who provided written consent prior to the start of the experiment. The experiment was approved by the Human Subjects Ethics Committee of the Kyoto Institute of Technology (Reference number: 2022-51) and conducted in accordance with the Declaration of Helsinki.

Statistical analyses were carried out by using SPSS 28 software (IBM Corp., United Status). A one-way analysis of variance (ANOVA) was used to analyse the differences in air permeability, padding thickness and impact force reduction amongst the samples. A repeated-measures ANOVA was conducted to assess the effect of different types of paddings on muscle activity. A Sidak pairwise comparison was conducted to evaluate the effect between two samples. The alpha level was set at 0.05 for statistical significance.

The results of the physical and mechanical tests are summarised in Fig. 6. Air permeability can affect the degree of wear comfort of garments and wearable products. A breathable material can promote the dispersal of heat by convection and the evaporation of sweat. Figure 6a shows that F1 has an air resistance of 2.4 kPa s/m, which is much higher than that of all of the knitted paddings, which means that it is more difficult for air to pass through this sample. F1 is made of neoprene with small holes punched into the material to increase breathability. F2 and F3 both consist of EVA and are thicker than F1. They also have a significantly higher level of air resistance that exceeds the range of the air permeability tester. The result shows that the knitted paddings are more air-permeable than the commercial paddings.

(a) Thickness and air resistance of samples, (b) compression stress–strain curves for all samples, (c) compression stress–strain curves for knitted padding samples with polyamide monofilament as spacer yarn, (d) compression stress–strain curves for knitted padding samples with polyester monofilament as spacer yarn, (e) ball-drop impact test set-up, (f) time-impact force curves of samples, and (g) impact force reduction of samples.

Although significant differences (p < 0.05) were found in the air permeability amongst the knitted samples, the differences are not very large when compared to the high air resistance of the commercial paddings. In comparing the samples with inlaid silicone tubes to the corresponding sample without an inlay, SPA and PA2 have the same measured air resistance of 0.17 kPa s/m. The measured air resistance of SPET is 0.16 kPa s/m which is significantly higher than that of PET2 of only 0.13 kPa s/m. The effect of the inlaid silicone tubes on air permeability is not remarkable when compared to the variations amongst the samples without an inlay: PA1, PA2, PET1, and PET2.

The thickness and stitch density are important physical properties for a 3D knitted fabric which affect the performance and wear comfort. The knitted padding samples have similar thicknesses. The thickness of PA1 is significantly less than that of PET2 and SPA (p < 0.05). No difference was found between PET2 and SPET or PA2 and SPA which means that the application of a silicone tube inlay does not have a significant impact on the thickness. It is observed that the irregular structure might have been affected when the silicone tubes were inserted into the middle layer of the padding by using tuck stitches. It was observed that the inlay does not change the wale density of the inner face and the course density of the outer face but increases the wale density of the outer face and the course density of the inner face. The silicone tubes provide additional connective strength between the two layers which would tend to flatten the structure of the padding. The differences between the densities of the two faces in both directions are therefore reduced. Therefore, although the knitted samples have similar thickness and shape, the mechanical properties could be different to affect their performance as a knee padding. It would be useful to understand how the change in 3D padding structure affects the compression behaviour and impact force absorption ability, so as to fabricate desired knee padding.

The compression test can provide a better understanding of the behaviour of the padding when the knee exerts pressure onto the padding. The compression stress–strain curves of all of the samples are presented in Fig. 6b. From the compression stress–strain curves, the Young’s modulus (E) of the paddings can be understood from the slopes of the curves in the linear elastic region as:

where σ is the stress and ɛ is the strain. A higher Young’s modulus indicates a stiffer material and deforms less under a given load. The energy absorption (W) of a material can be determined by the area under the stress–strain curves:

where V is the volume and ɛf is the strain at stress of 49 kPa. It is expected that materials with a larger area under the stress–strain curve can absorb more impact force.

Both PET and PA monofilaments are commonly used as connective yarns of spacer fabrics. The samples made with PET monofilaments have a higher compression strength than those made of PA monofilaments. The results of the compression test also showed that an increase in the thickness of the spacer yarn increases the compression stiffness of the resultant spacer fabric. This finding is in agreement with that of previous studies27,33.

On the other hand, it is interesting to find that the knitted paddings with a silicone tube inlay reduce the initial compression stiffness showing a lower slope on the stress–strain curve (Fig. 6c,d). In Yu et al.26, the use of a silicone tube inlay in spacer fabric provides better support to the flat 3D fabric structure, increases the compression strength and energy absorption and increases the ability of the fabric to withstand higher levels of stress before entering the plateau stage of the stress–strain curve. However, silicone tubes inserted into a curved and irregularly shaped 3D knitted padding instead of a flat and more uniformly shaped fabric impact the compression stress–strain behaviour. At the initial stage of the compression, the compression stress of SPA and SPET is lower than that of PA1, PA2, PET1 and PET2. That is, the samples with a silicone tube inlay are softer and compress more easily when the compression stress is below 5 kPa. When the compression continues, both SPA and SPET show an increase in the slopes of the stress–strain curves, which indicates that it is more difficult to further compress them. The slopes of the curves are further increased when the compression strain exceeds 0.5 for both SPA and SPET. The stress–strain curves showed a larger slope at the beginning of the compression followed by a decrease or even a noticeable plateau for the sample without an inlay. Similar to spacer fabrics, the monofilament yarns in the middle layer play an important role in supporting the three-layer knitted structure. When the compression increases to a certain degree that causes buckling and shearing of the monofilament yarns, the spacer structure will collapse and a flatter slope of the stress–strain curve could be observed. The distribution of the tucking points of the monofilament yarns on the two faces differs due to the irregular structure of the padding. The curved spacer fabric has a large number of courses in the outer face meaning a lower ratio of monofilament yarns to courses, thus making the padding less stable compared to a flat spacer fabric that is more regular in structure. When additional silicone tubes are inserted into the middle layer, the surface becomes curvy due to the tuck stitches of the silicone tube, the alignment of the monofilament yarns is further affected, and the structure is even less supported. Therefore, the padding becomes softer and more easily compressed by using a small amount of force. On the other hand, when the compression force is further increased, the monofilaments buckle and silicone tubes are then the primary support of the structure. Therefore, instead of showing a decrease in slope or a plateau of the stress–strain curve, the padding increases in compression stiffness.

With respect to the commercial padding samples, significant differences in the compression stiffness and energy absorption ability can be observed due to the difference in materials and thickness. There is no standardised stiffness for knee paddings. F3 is the most difficult to compress with the least energy absorption followed by F2 and then F1. F1 has a low compression strength at a strain from 0 to 0.15 due to the presence of a layer of soft knitted fabric. F2 and F3 are much more rigid, lower amount of energy absorption and more difficult to compress compared to the knitted samples in the compression test. All of the commercial samples have a higher compression stiffness that can only be compressed to a lower strain at a compression stress of 49 kPa.

The ball drop impact test replicates an external force exerted onto the knee padding, which was carried out to understand how much the padding samples can absorb impact force. The test set-up, plotted time vs. impact force, and percentage of impact force reduction are presented in Fig. 6e–g respectively.

At the time of the ball just before reaching the padding sample, assuming air resistance is negligible, the kinetic energy (KE) of the ball can be calculated by using:

where m is the mass and v0 is the velocity of the ball.

Based on the law of conservation of energy, the velocity can be expressed as:

where g is the acceleration due to gravity and h is the travelling distance of the ball.

During the collision, the ball pushes the padding and then returns to the surface of the padding. If there is no energy consumed by the padding, the relationship between the impulse and the change of momentum becomes:

where F is the impact force and t is the elapsed time.

However, the collision could lead to the deformation of padding and thus some of the kinetic energy is absorbed by the padding. The impact force changes with time and a change in momentum (Ic) as absorbed kinetic energy are considered as:

From Eq. (7), the impact force is inversely proportional to the elapsed time. The padding that can bring a larger change in momentum and hence the absorption of kinetic energy could bring a lower impact force and a longer elapsed time.

The FR of the knitted padding samples is similar without statistically significant differences (p > 0.05) between PET1 and PET2, and PA1 and PA2. The difference in the thickness of the monofilament yarns used in the middle layer does not have a significant effect on the impact force reduction ability of the padding in the test. As PET2 and PA2 show a higher energy absorption in the compression test than PET1 and PA1 respectively, it is expected that the FR would be higher for PET2 and PA2. The four knitted samples without a silicone inlay show relatively large energy absorption in the compression test but have lower FRs than the other padding samples. This could be because the soft knitted samples fail to withstand the impact force from the ball dropped and collapse completely to allow the rest of the impact force to hit the load cell. On the other hand, the paddings with a silicone inlay show a significant increase (p < 0.05) in FR compared to the paddings without an inlay.

This further shows that the silicone inlay can better support the padding structure and therefore more effective in reducing the impact force. Thus, the knitted padding with a silicone inlay is a better option as a cushioning material and for protective purposes. SPET can provide an FR of 71.1% which increases from PET2 by 14%. The increment of FR of SPA from PA2 is only 5.5%. The silicone inlay is more effective in enhancing the impact force absorption on the 3D knitted structure made of PET monofilament.

As for the commercial paddings, F2 reduces the highest amount of exerted force, with relatively flat time-impact force curves for the ball drop test. F3 also shows a good ability to reduce the impact force in comparison to all of the knitted samples. This aligns with the compression test results that F2 has lower stiffness and higher energy absorption than F3. However, F1 has a similar ability as some of the knitted samples to reduce the force or even a more poor performance. There is no significant difference (p > 0.05) in the ability to reduce the impact force amongst F1, PA1 and PA2. SPET and SPA have a significantly higher ability to reduce the impact force in comparison to F1. The commercial products vary greatly in thickness, compression behaviour and ability to absorb impact force. The protection performance and requirements for knee sleeves are unclear and there is a lack of related information provided to consumers. Further investigation into knee paddings in terms of the end-uses is recommended to allow suitable and sufficient protection to the knees during sporting activities.

The knitted padding with the best performance in impact force absorption is SPET, which was used in a wear trial for comparison with the three other commercial paddings. As two plies of knitted padding were used in the impact force test which showed a comparable impact force reduction as that of the commercial paddings, two plies of SPET were used in the wear trial to align with the evaluation condition. Figure 7a and b present the subjective rating results. Before carrying out the three exercises with the different knee paddings, F1 was found to have the highest rating in softness, elasticity, bendability, fit and wear comfort, followed by the 2-ply SPET, F2 and finally, F3, which has the lowest rating. After the exercises, the ranking remained unchanged for these five aspects.

Subject ratings of knee padding samples: (a) before and (b) after exercising and activity of different muscles under different knee padding conditions with: (c) pre-running walking, (d) running, (e) post-running walking, (f) jumping and (g) squatting.

F2 is the most thick and relatively hard and rigid as the compression results show, which can be the reason for the lowest ratings of softness, elasticity, bendability, fit and wear comfort. The 2-ply SPET has a similar thickness as F2. Although 2-ply SPET is not ranked the highest amongst the samples, nevertheless, this sample has a much more outstanding performance than F2 and F3. The rating of the wear comfort of the 2-ply SPET is actually very close to that of F1 which is a relatively thin padding. This indicates the potential of using knitted padding to enhance wear comfort.

On the other hand, an interesting observation was found in the rating of slippage. Prior to the exercises, the 2-ply SPET received the highest rating for slippage which means that the user perceived that this material is not slip resistant. However, the 2-ply SPET received the lowest rating for slippage after the exercises were completed. The 2-ply SPET padding is thick and bulky, which could give the initial impression that it will easily slip. After the participants donned this knee padding for the different exercises, they found that the slippage was much less than expected. On the other hand, the slippage ratings increased for F1, F2 and F3. Therefore, the knitted structure imparts flexibility, which allows the paddings to resist slipping more than the commercial paddings tested. This shows the advantages of the 3D knitted padding for knee protection. Therefore, a follow-up study that further investigates the relationship between slippage during use and the flexibility and extensibility of the knitted padding is recommended to confirm that the elastic knitted padding does not easily slip.

sEMG was used to measure the muscle activity during the exercises in the wear trial. The %MVE values of the different exercises are presented in Fig. 7c–g. The results of the repeated-measures ANOVA showed that there is a significant difference between the different knee padding conditions on the BF muscles during running. Although there is no statistically significant difference found in the pairwise comparison, it can be observed that there is more muscle activity of the BF muscle under the 2-ply SPET padding than in the other conditions during running. This is likely because more force and contraction of the BF muscle are needed to stretch the knitted padding with the flexion of the knee during running. On the other hand, no significant differences (p < 0.05) can be found between the different knee padding conditions in the muscle activity of the VL, BF and GL muscles during the other activities. This indicates that wearing knee sleeves with different types of padding materials would not create an additional burden to the wearers during the wear trial exercises.

Nevertheless, some limitations of the wear trial assessment are noted. The physical activities for the wear trial do not fully cover the wide range of activities and sports that require the use of knee pads. The duration and intensity of the exercises are relatively lower compared to a formal sporting activity. Therefore, the findings on the impact of muscle activity do not reflect the actual use of knee sleeves and paddings in sports competitions but serve to provide an initial understanding of the effect on different knee and leg movements. In further work on knee paddings and protective devices, it is recommended that a wear trial be carried out with professional athletes during their daily training routine to examine the physiological, psychological and psychophysical influences.

With the large range and complexities of joint motions, it is challenging to develop knee paddings that offer a good wear experience. The material used as the padding of knee braces or knee sleeves has to be soft and flexible enough to accommodate the body contours and not limit the range of motion of the joints, be air permeable enough to enhance wear comfort and absorb impact forces well enough to sufficiently protect the body. This study has developed a novel 3D three-layer knitted padding for protecting the knees. Knitted padding samples made with different types of monofilament yarns and a silicone tube inlay to support the 3D structure have been fabricated and evaluated. Through objective and wear trial evaluations and comparisons done with three commercially available knee padding samples, the following findings are identified:

The air permeability of the 3D knitted paddings excels the currently available knee paddings made with elastomeric material.

A lower initial compression stiffness and increased compression strength when compression stress is increased can be achieved by applying silicone inlay in a 3D knitted padding.

The spacer samples made with PET monofilaments have a higher compression strength comparing with those made of PA monofilaments in regardless of the presence of silicone inlay.

The knitted padding with a silicone tube inlay improves the impact force reduction by 14% and 5.5% for spacer fabric samples made of PET and PA respectively, making it comparable to that of commercial paddings.

The novel knitted padding provides greater perceived softness, elasticity, bendability, fit and wear comfort than two of the commercial paddings of similar thickness while offering the best slip resistance amongst all the tested commercial paddings.

During running, the knitted padding increases muscle activation (MVE%) in the BF muscle, although no significant differences are observed during walking, jumping, and squatting across different samples.

The findings show the advantages of using the developed 3D knitted padding for knee protection, especially in terms of the perceived softness, air permeability and slip resistance. The potential and feasibility of the production of 3D knitted padding are also demonstrated. The knitted padding can also be knitted into different shapes to accommodate the contours of different body parts to provide cushioning for different wearable protection products. Although there is still some insufficiency in impact force reduction which affects the protective function of the knitted padding compared to the elastomeric materials, further work on the knit structure, inlaid materials and inlay methods need to be carried out to enhance the performance.

Data is provided within the manuscript.

Obi, B. E. In Polymeric Foams Structure–Property–Performance (ed. Obi, B. E.) 299–331 (William Andrew Publishing, 2018).

Chapter Google Scholar

Yoneda, M., Nakajima, C. & Inoue, T. Compression-recovery properties and compressive viscoelastic properties of polyurethane foam for cushioning material for home furnishings use. J. Jpn. Res. Assoc. Text. End Uses 55, 61–68 (2014).

Google Scholar

Jin, F.-L., Zhao, M., Park, M. & Park, S.-J. Recent trends of foaming in polymer processing: A review. Polymers 11, 953 (2019).

Article PubMed PubMed Central Google Scholar

Landrock, A. H. Handbook of Plastic Foams: Types, Properties, Manufacture and Applications (Elsevier, 1995).

Google Scholar

Dalaq, A. S., Khazaaleh, S. & Daqaq, M. F. An origami-inspired design of highly efficient cellular cushion materials. Appl. Mater. Today 32, 101835. https://doi.org/10.1016/j.apmt.2023.101835 (2023).

Article Google Scholar

Hua, X. & Shu, L. In Cartilage Tissue and Knee Joint Biomechanics (eds Nochehdehi, A. R. et al.) 313–334 (Academic Press, 2024).

Chapter Google Scholar

Duivenvoorden, T. et al. Braces and orthoses for treating osteoarthritis of the knee. Cochrane Database Syst. Rev. https://doi.org/10.1002/14651858.CD004020.pub3 (2015).

Article PubMed PubMed Central Google Scholar

Moon, J., Kim, H., Lee, J. & Panday, S. B. Effect of wearing a knee brace or sleeve on the knee joint and anterior cruciate ligament force during drop jumps: A clinical intervention study. Knee 25, 1009–1015. https://doi.org/10.1016/j.knee.2018.07.017 (2018).

Article PubMed Google Scholar

Siebers, H. L., Eschweiler, J., Pinz, J., Tingart, M. & Rath, B. The effect of a knee brace in dynamic motion—An instrumented gait analysis. PLoS ONE 15, e0238722. https://doi.org/10.1371/journal.pone.0238722 (2020).

Article PubMed PubMed Central Google Scholar

Pierrat, B. et al. Characterisation of knee brace migration and associated skin deformation during flexion by full-field measurements. Exp. Mech. 55, 349–360. https://doi.org/10.1007/s11340-014-9947-2 (2015).

Article Google Scholar

Liu, Y., Hu, H., Long, H. & Zhao, L. Impact compressive behavior of warp-knitted spacer fabrics for protective applications. Text. Res. J. 82, 773–788 (2012).

Article Google Scholar

Yip, J. & Ng, S.-P. Study of three-dimensional spacer fabrics: Physical and mechanical properties. J. Mater. Process. Technol. 206, 359–364. https://doi.org/10.1016/j.jmatprotec.2007.12.073 (2008).

Article Google Scholar

Li, N. W., Yick, K. L., Yu, A. & Ning, S. Mechanical and thermal behaviours of weft-knitted spacer fabric structure with inlays for insole applications. Polymers 14, 619. https://doi.org/10.3390/polym14030619 (2022).

Article PubMed PubMed Central Google Scholar

Yu, A. & Sukigara, S. Investigation of materials for palm and dorsal of anti-vibration gloves for thermal comfort. Fash. Text. 10, 21. https://doi.org/10.1186/s40691-023-00340-0 (2023).

Article Google Scholar

Yick, K. L. et al. In Textile Bioengineering and Informatics Symposium Proceedings 2014—7th Textile Bioengineering and Informatics Symposium, TBIS 2014, in conjunction with the 5th Asian Protective Clothing Conference, APCC 2014, 219–224.

Yu, A., Shirakihara, M., Yick, K. L., Sukigara, S. & Chan, K. C. Development of fully fashioned knitted spacer fabric bra cup: One-step production from yarn. Mater. Des. 219, 110825. https://doi.org/10.1016/j.matdes.2022.110825 (2022).

Article Google Scholar

Guo, Y. et al. Comparing properties of the Warp-knitted spacer fabric instead of sponge for automobile seat fabric. J. Phys. Conf. Ser. 1948, 012196. https://doi.org/10.1088/1742-6596/1948/1/012196 (2021).

Article Google Scholar

Yu, A., Li, P. L., Yick, K. L., Ng, S. P. & Yip, J. N. Investigation of microclimate in sports shoes with the integration of human subjective sensations. Key Eng. Mater. 765, 140–146 (2018).

Article Google Scholar

Liu, Y., Hu, H., Zhao, L. & Long, H. Compression behavior of warp-knitted spacer fabrics for cushioning applications. Text. Res. J. 82, 11–20 (2012).

Article Google Scholar

Liu, Y. & Hu, H. Compression property and air permeability of weft-knitted spacer fabrics. J. Text. Inst. 102, 366–372 (2011).

Article Google Scholar

Asayesh, A. & Amini, M. Analysis of the compression performance of weft-knitted spacer fabrics for protective applications in view of the surface layer structure. Fibers Polym. 22, 3469–3478. https://doi.org/10.1007/s12221-021-0248-y (2021).

Article Google Scholar

Hamedi, M., Salimi, P. & Jamshidi, N. Improving cushioning properties of a 3D weft knitted spacer fabric in a novel design with NiTi monofilaments. J. Ind. Text. 49, 1389–1410. https://doi.org/10.1177/1528083718817560 (2020).

Article Google Scholar

Jiang, S., Ding, M., Chen, W. & Wang, J. Preparation and properties of flexible cushioning composites based on silicone rubber and warp—Knitted spacer fabric. Silicon 15, 3323–3338. https://doi.org/10.1007/s12633-022-02267-5 (2023).

Article Google Scholar

Xu, W., Yan, B., Hu, D. & Ma, P. Preparation of auxetic warp-knitted spacer fabric impregnated with shear thickening fluid for low-velocity impact resistance. J. Ind. Text. 51, 7188S-7204S. https://doi.org/10.1177/1528083720927013 (2020).

Article Google Scholar

Yu, A., Sukigara, S. & Takeuchi, S. Effect of inlaid elastic yarns and inlay pattern on physical properties and compression behaviour of weft-knitted spacer fabric. J. Ind. Text. 51, 2688S-2708S. https://doi.org/10.1177/1528083720947740 (2022).

Article Google Scholar

Yu, A., Sukigara, S. & Shirakihara, M. Effect of silicone inlaid materials on reinforcing compressive strength of weft-knitted spacer fabric for cushioning applications. Polymers 13, 3645. https://doi.org/10.3390/polym13213645 (2021).

Article PubMed PubMed Central Google Scholar

Yu, A., Sukigara, S., Yick, K. L. & Li, P. L. Novel weft-knitted spacer structure with silicone tube inlay for enhancing mechanical behavior. Mech. Adv. Mater. Struct. 29, 2053–2064. https://doi.org/10.1080/15376494.2020.1850948 (2020).

Article Google Scholar

Yu, A., Sukigara, S. & Yick, K. L. Curvature control of weft-knitted spacer fabric through elastic inlay. Text. Res. J. https://doi.org/10.1177/00405175221097098 (2022).

Article Google Scholar

Sakamoto, A., Khan, M. T. I. & Kurita, T. In 2015 4th International Conference on Informatics, Electronics and Vision, ICIEV (2015).

Piazza, S. J. & Delp, S. L. The influence of muscles on knee flexion during the swing phase of gait. J. Biomech. 29, 723–733 (1996).

Article PubMed Google Scholar

Konrad, P. The ABC of EMG. A Practical Introduction to Kinesiological Electromyography Vol. 1, 30–35 (Noraxon, 2005).

Google Scholar

Ziv, G. & Lidor, R. Vertical jump in female and male basketball players—A review of observational and experimental studies. J. Sci. Med. Sport 13, 332–339 (2010).

Article PubMed Google Scholar

Zhao, T., Long, H., Yang, T. & Liu, Y. Cushioning properties of weft-knitted spacer fabrics. Text. Res. J. 88, 1628–1640. https://doi.org/10.1177/0040517517705630 (2018).

Article Google Scholar

Download references

This study was supported by the Kyoto Technoscience Centre and Start-up Fund from the Hong Kong Polytechnic University.

ST709, School of Fashion and Textiles, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong

Annie Yu

Faculty of Fiber Science and Engineering, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto, 606-8585, Japan

Yijia Zhang

Faculty of Textile Science and Technology, Shinshu University, 3 Chome-15-1 Tokida, Ueda, Nagano, 386-8567, Japan

Shunji Takeuchi

You can also search for this author inPubMed Google Scholar

You can also search for this author inPubMed Google Scholar

You can also search for this author inPubMed Google Scholar

A.Y. contributed the concept, design and development of prototypes, performed the experiments and data analysis, supervised the study and wrote the manuscript. Y. Z. contributed to experiment and data collection. S.T. contributed to the design of experiment. All the authors reviewed the manuscript.

Correspondence to Annie Yu.

The authors declare no competing interests.

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.

Reprints and permissions

Yu, A., Zhang, Y. & Takeuchi, S. Advanced design of 3D knitted padding for wearable cushioning in knee protector. Sci Rep 15, 11091 (2025). https://doi.org/10.1038/s41598-025-92552-1

Download citation

Received: 11 September 2024

Accepted: 28 February 2025

Published: 01 April 2025

DOI: https://doi.org/10.1038/s41598-025-92552-1

Anyone you share the following link with will be able to read this content:

Sorry, a shareable link is not currently available for this article.

Provided by the Springer Nature SharedIt content-sharing initiative